The only upside from this from my point of view (a recent RX 470 owner on Arch) is that Linux drivers are likely very close to "just working". Currently somethings have just made their way in to the kernel (Audio bitstreaming, 4.11 I think, and I think I saw it first hand I was running the 4.11 release candidate a few days ago) and soon FreeSync (FWIW) and HDCP are coming soon.
Upside: No proprietary kernel blobs. I applaud AMD on this front and it completely motivated my purchasing decision of my RX 470 (vs nVidia 1060).